The present invention relates to a method of operating a rotary or similar furnace which contains a controlled atmosphere and is equipped with a furnace door through which the parts being treated under said controlled atmosphere are fed into and removed from the furnace chamber, which contains said controlled atmosphere, by means of a feeding and removal device.
It is well known that rotary or other furnaces for heat treating turbine blades or other materials must have a controlled atmosphere. Conventional rotary furnaces are only equipped with one opening for charging or feeding the parts to be treated into, and removing the parts having been treated from, the controlled atmosphere furnace chamber, said opening being closed by a furnace door during the heat treating process. Because of the relatively large size that any such furnace opening for feeding and removing parts to be treated must have, oxygen from the ambient air will enter and mix with the furnace atmosphere when the furnace door is opened, unless complex precautions are taken. Even a furnace vestibule located immediately in front of the furnace door and fitted with a vestibule entry door would not adequately prevent any such entry of oxygen into the furnace chamber, because the feeding and removal device which carries the part to be heat treated or having been heat treated would have to move through the open vestibule door and the open furnace door for feeding said part for treatment or removing said part after treatment, thus at the same time allowing ambient air to enter the controlled furnace atmosphere. If such a furnace were protected by flushing controlled atmosphere from the furnace chamber into any such vestibule to prevent the entry of oxygen while the furnace door and the vestibule entry door are open, the quantity of controlled atmosphere, needed for the protection of the furnace atmosphere by the technique described, would be too high for a cost efficient or economical heat treatment.
It is therefore an object of the present invention to provide a comparatively simple method of reliably preventing the entry of oxygen into the controlled atmosphere in the furnace chamber of a rotary or similar furnace of the aforementioned general type without increasing the volume of controlled atmosphere required for the operation of such a furnace beyond the limits set by a cost efficient and economical heat treatment.